Methods: TetOn lentiviral particles encoding for IGF-1 and the Tet-transactivator (tTA) were cloned and used to stably transduce human foreskin fibroblasts (HFF). Baseline and doxycycline induced IGF-1 release from HFFTetOn+IGF1 was quantified by ELISA. HFFwt and HFFTetOn+IGF1 conditioned medium was layered over human embryonic stem cell (HES2) derived cardiomyocytes followed by an analysis of AKT-phosphorylation. EHMs were assembled from HES2-derived cardiomyocytes and HFF (HFFwt or HFFTetOn+IGF1) at 70:30 ratio. Transgene activation was induced by addition of doxycycline (10 ng/ml) for 7 days. Twitch forces and response to pharmacological stimuli were measured to assess the functional consequences of IGF-1 release. EHMs were subsequently subjected to morphological analysis or dissociated into single cells to assess cellular composition of EHMs.

Conclusion: EHM can be functionally enhanced by integration of drug-controllable IGF-1 release. Drug controllable, cell based paracrine release of protective factors may not only be exploited to enhance tissue engineered myocardium in vitro but also to achieve better survival and integration of EHM grafts in vivo.